EP1662738B1 - Dispositif et procédé de détection de début de trame - Google Patents

Dispositif et procédé de détection de début de trame Download PDF

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Publication number
EP1662738B1
EP1662738B1 EP05026009.0A EP05026009A EP1662738B1 EP 1662738 B1 EP1662738 B1 EP 1662738B1 EP 05026009 A EP05026009 A EP 05026009A EP 1662738 B1 EP1662738 B1 EP 1662738B1
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Prior art keywords
frame
counter value
cyclic prefix
mode
interval
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German (de)
English (en)
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EP1662738A3 (fr
EP1662738A2 (fr
Inventor
In-Hyoung Kim
Tae-Gon Kim
Yun-Sang Park
Bong-Gee Song
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Samsung Electronics Co Ltd
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Samsung Electronics Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2673—Details of algorithms characterised by synchronisation parameters
    • H04L27/2676—Blind, i.e. without using known symbols
    • H04L27/2678—Blind, i.e. without using known symbols using cyclostationarities, e.g. cyclic prefix or postfix
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation

Definitions

  • the present invention relates to an apparatus and method for acquiring synchronization using periodically repeated patterns of a preamble.
  • a transmitter transmits a synchronization signal to a receiver and the receiver acquires synchronization using the received synchronization signal.
  • the standardization committee for the IEEE 802.16 standard has recently suggested a communication system adopting an Orthogonal Frequency Division Multiple Access (OFDMA) technique for high-speed data transmission.
  • OFDMA Orthogonal Frequency Division Multiple Access
  • a transmitter transmits a preamble pattern to a receiver and the receiver acquires the start point of a frame, i.e., frame synchronization, using the received preamble pattern.
  • FIG. 1 illustrates a preamble pattern used for initial synchronization in a communication system.
  • a preamble 10 includes repeated patterns 12, 13, and 14 and a cyclic prefix (CP) 11.
  • CP cyclic prefix
  • OFDM Orthogonal Frequency Division Multiplexed
  • a guard interval that is longer than a maximum delay spread of the multipath channel is inserted between consecutive OFDM symbols.
  • the last part of a valid symbol interval is copied and inserted into the guard interval, which is called a cyclic prefix.
  • the structure of an apparatus for estimating the start of a frame is as shown in FIG. 2 .
  • W and D can be selected from among several values according to the structure of a preamble and the way of implementing the preamble. For example, when a preamble includes 3 repeated patterns, W may be equal to 2L+CP and D may be equal to L
  • CP is the length of cyclic prefix.
  • FIG. 2 is a block diagram illustrating a conventional apparatus for estimating the start of a frame.
  • the apparatus for estimating the start of a frame includes a conjugator 22, a first delayer 24, a correlator 26, a second delayer 28, a summer 30, and a third delayer 32.
  • the conjugator 22 calculates the conjugate of a received signal and outputs the conjugate to the correlator 26.
  • the first delayer 24 delays a received signal by a repetition interval of L and outputs the delayed signal to the correlator 26.
  • the correlator 26 calculates a correlation between the received signal and the delayed signal and outputs the correlation to the summer 30 and to the second delayer 28.
  • the second delayer 28 delays the correlation output from the correlator 26 by a window size W of a preamble and outputs the delayed correlation to the summer 30.
  • the summer 30 sums the correlation output from the correlator 26 and the delayed correlation output from the second delayer 28.
  • the third delayer 32 delays a value output from the summer 30 by 1 (sample) and outputs the result to the summer 30. Since the output of the second delayer 28 is subtracted from a value resulting from operations of the third delayer 32 and the summer 30 that continuously sum outputs of the correlator 26, the second delayer 28, the third delayer 32 and the summer 30 function together to sum up the outputs of the correlator 26 only during a W of a preamble.
  • Equation 1 The correlation is determined by Equation 1 as follows.
  • r(n) is a received signal
  • C(n) is autocorrelation function of the received signal r(n) at time index n
  • D is delay in autocorrelation function
  • W is window size in autocorrelation function.
  • n 0 is the start point of a frame
  • the start point of a preamble i.e., the start point of the frame, can be estimated by searching for a position in which
  • Such a conventional technique is based on the assumption that a preamble is comprised of repeated patterns of a signal having a length of L. This assumption cannot be satisfied when a high-level interference signal is input.
  • a 0 should be periodically inserted between transmission signals in a frequency domain and the transmission signals should be converted into time-domain signals through inverse fast Fourier transform (IFFT) for transmission.
  • IFFT inverse fast Fourier transform
  • a signal is inserted into only one of three subcarriers, and the other two subcarriers are each filled with a "0" and then undergo an IFFT.
  • the preamble includes three repeated patterns.
  • FIG. 3 is a graph illustrating the use of frequencies and their respective sectors in a multi-sector environment in a wireless communication system.
  • a cell can be divided into a plurality of sectors.
  • Each sector has three repeated patterns by inserting a signal into only one of three subcarriers and filling the other two subcarriers with 0s and performing IFFT on the two subcarriers in a frequency domain.
  • signals of sectors are mixed at the boundary between the sectors. Therefore, a received signal may actually include signals from more than the sector and may even contain signals from all three sectors, thus, increasing the likelihood of receiving a signal other than a 0.
  • frequency-domain signals having no 0s are filled in all the subcarriers, causing weakening of a repeated pattern of a time-domain signal.
  • conventional techniques based on the repeated pattern of the time-domain signal experience severe performance degradation.
  • an object of the present invention to provide an apparatus and method for estimating a start of a frame, which can compensate for performance degradation caused by an interference signal between sectors in a multi-sector environment.
  • the invention is defined by the appended claims.
  • FIGs. 4 through 7 A configuration and operation of an apparatus for estimating a start of a frame according to an embodiment of the present invention will now be described with reference to FIGs. 4 through 7 .
  • FIG. 4 is a block diagram illustrating an apparatus for estimating the start of a frame according to a preferred embodiment of the present invention.
  • the apparatus for estimating the start of a frame includes a correlator 110 having a variable window size and a variable delay, a maximum value point output unit 120 for returning (or outputting) the relative position of the maximum value among values input during a predetermined time interval, an algorithm control block 140 for controlling the apparatus, a counter 150 whose maximum value is equal to the number of samples (T S ) of a frame, and a final point output unit 130 for combining outputs of the maximum value point output unit 120 and outputting a start point of a final frame.
  • FIG. 5 is a diagram illustrating a general frame structure including a preamble and OFDM symbols.
  • a frame includes a downlink frame 200 and an uplink frame 300.
  • a subscriber station receives the downlink frame 200 from a base station (not shown) and transmits the uplink frame 300 to the base station.
  • the downlink frame 200 includes a preamble 210 and OFDM symbols 220.
  • the preamble 210 includes a cyclic prefix (CP) 211 and repeated patterns 212, 213, and 214.
  • the cyclic prefix 211 has a window size CP and each of the repeated patterns 212, 213, and 214 has a window size L.
  • the apparatus for estimating the start of a frame estimates the start of a frame by calculating a correlation between preambles upon receipt of a frame and searching for an interval or point of time during or at which the correlation is maximal.
  • the apparatus for estimating the start of a frame also uses a cyclic prefix to accurately estimate the start of a frame. As shown in FIG. 5 , the cyclic prefix is included in the preamble 210 and/or the OFDM symbols 220. A signal corresponding to an interval of the cyclic prefix is copied from the last part of a valid symbol interval and is inserted into the preamble 210 or the OFDM symbols 220.
  • a cyclic prefix is the same as the last interval of a preamble or an OFDM symbol. Therefore, an intervalor point of time during or at which a correlation between a cyclic prefix and the last interval of a preamble or an OFDM symbol is maximal can be estimated as the start position of a cyclic prefix.
  • the present invention provides reliability in estimation of the start point of a frame by estimating the start of a preamble in a downlink frame and the start of a cyclic prefix of a preamble.
  • the correlator 110 operates in two operation modes designated herein as mode 1 and mode 2.
  • Mode 1 is an operation mode for estimating the start of a frame
  • mode 2 is an operation mode for estimating the start of a cyclic prefix.
  • the start position of a frame can be detected by implementing only mode 1.
  • mode 2 it is also possible to more accurately detect the start position of a frame by implementing mode 2 within a predetermined error range estimated based on the start position of a frame resulting from the implementation of mode 1.
  • FIG. 6 is a diagram illustrating output results in different operation modes of the correlator 110 according to an embodiment of the present invention.
  • the correlator 110 outputs the maximum correlation at the start position of each frame in mode 1 and outputs the maximum correlation at the start position of a cyclic prefix of a preamble or symbol in mode 2.
  • the correlator 110 generates the maximum correlation only at the start position of a frame during the correlator's operation in the mode 1 and generates the maximum correlation at the start point of each symbol during the correlator's operation in mode 2.
  • the maximum correlation in the mode 1 is sensitive due to an interference signal caused by neighbor sectors, the estimation performance is degraded.
  • an interference signal caused by neighbor sectors also has a symbol structure having a cyclic prefix, the estimation performance using the maximum correlation in mode 2 is not affected by the interference signal caused by neighbor sectors.
  • a start point of a final frame is searched in a combination of the two modes.
  • the correlator 110 has a window size required to sum correlations between repeated patterns of a preamble in mode 1 and a delay for correlation that is equal to an interval of each of the repeated patterns. For example, when there are three repeated patterns as shown in FIG. 5 , the correlator 110 has a window size of 2L+CP and a delay ofL in mode 1. Moreover, the correlator 110 sums a correlation between the repeated patterns 212 and 213 and a correlation between the repeated patterns 213 and 214 in mode 1 during 2L. The correlator 110 then delays each of the repeated patterns 212, 213, and 214 by the interval of each of the repeated patterns 212, 213, and 214, i.e., L, to acquire corresponding correlations. Thus, the correlator 110 can estimate the start of a preamble in the downlink frame 200, i.e., the start of a frame, in mode 1.
  • the correlator 110 has a window size required to sum correlations between cyclic prefixes in mode 2, and a delay for correlation is equal to an interval in a preamble or symbol between a cyclic prefix and an interval that is the same as the cyclic prefix. For example, in the case of an OFDM symbol 220 shown in FIG. 5 , the correlator 110 has a window size CP and a delay N.
  • the correlator 110 sums a correlation between the cyclic prefix 211 and an interval that is the same as the cyclic prefix 211 and a correlation between the cyclic prefix 221 and an interval that is the same as the cyclic prefix 221 during CP in mode 2.
  • the correlator 110 also delays the cyclic prefixes 211 and 221 by N to acquire a correlation therebetween.
  • the correlator 110 can estimate the start of a cyclic prefix of a preamble or symbol in mode 2.
  • the counter 150 increases a counter value by 1 for every sample throughout the entire algorithm execution interval and is reset to 0 when a counter value reaches a value corresponding to a frame interval T s .
  • the counter 150 provides the counter value to the algorithm control block 140 and the maximum value point output unit 120.
  • the maximum value point output unit 120 receives a counter value from the counter 150 and a correlation from the correlator 110 and outputs a counter value at which the correlation is maximal during a frame interval to the algorithm control block 140.
  • FIG. 7 is a diagram illustrating an operation of the apparatus for estimating the start of a frame according to an embodiment of the present invention.
  • the algorithm control block 140 controls the correlator 110 to operate in each of the operation modes.
  • the algorithm control block 140 controls the correlator 110 to operate during an initial frame interval in mode 1.
  • mode 1 the correlator 110 calculates a correlation between repeated patterns of a preamble and outputs the correlation.
  • the maximum value point output unit 120 outputs a counter value n 0 at which the correlation is maximal to the algorithm control block 140, as shown in FIG. 7 .
  • the algorithm control block 140 receives the counter value n 0 from the maximum value point output unit 120.
  • the algorithm control block 140 then resets a counter value to 0 when the counter value reaches n 0 -T e during the next frame interval.
  • T e is an error range of an estimated value. More specifically, n 0 represents a counter value at which a correlation is maximal during a frame interval. A point at which the correlation is maximal is estimated as the start point of a frame, and n 0 has an error range of ⁇ T e based on the error range of the estimated start point.
  • the algorithm control block 140 controls the correlator 110 to operate in mode 2 in a counter value range of [0, 2T e ].
  • [0, 2T e ] is a range of 0 to 2T e .
  • the correlator 110 operates in mode 2 from a counter value n 0 -T e to a counter value n 0 +T e .
  • the correlator 110 calculates a correlation between a cyclic prefix and the last interval of a preamble or symbol, which is the same as the cyclic prefix, and outputs the correlation.
  • the maximum value point output unit 120 outputs a counter value n 1 at which the calculated correlation is maximal to the final point output unit 130.
  • the algorithm control block 140 then controls the correlator 110 to operate in the mode 2 during an interval of [N+CP, 2T e +N+CP] of the next symbol to acquire a correlation with the next cyclic prefix.
  • the maximum value point output unit 120 outputs a counter value n 2 at which the correlation is maximal to the final point output unit 130.
  • the algorithm control block 140 controls the correlator 110 to operate in mode 2 during an interval of [2*(N+CP), 2T e +2*(N+CP)] of the next symbol and to output a counter value n 3 at which the correlation is maximal to the final point output unit 130. In this way, the algorithm control block 140 estimates the start point of a cyclic prefix for up to (M-1) symbols.
  • the final point output unit 130 combines estimated start points of a cyclic prefix, which are output from the maximum value point output unit 120, using Equation 2 to estimate a start point of a final frame n ⁇ f
  • n ⁇ f is defined by Equation 2 as follows.
  • M indicates the number of estimated start points of a cyclic prefix
  • CP indicates an interval of a cyclic prefix
  • N indicates an interval of a preamble or symbol excluding CP
  • N+CP indicates the entire interval of a preamble or symbol
  • n m indicates each of the estimated start points of a cyclic prefix.
  • M is the number of observation OFDM symbols. This is smaller than the number of OFDM symbols in one frame. If a counter value is reset to 0 at a finally estimated start point, the counter value 0 may be the start point of a frame.
  • FIG. 8 is a flowchart illustrating a method for estimating the start of a frame according to an embodiment of the present invention.
  • the apparatus for estimating the start of a frame determines whether the received frame is the first frame whose start point to be estimated in step 310. If so, the frame start estimation apparatus proceeds to step 320 to estimate the start point of the frame.
  • the start point of a frame is estimated by calculating a correlation between preambles and searching for an interval or point of time during or at which the calculated correlation is maximal.
  • the frame start estimation apparatus then proceeds to step 330 to determine whether the next frame is received. If so, the frame start estimation apparatus proceeds to step 340 to estimate the start point of a cyclic prefix around the estimated start point of the frame. In other words, the frame start estimation apparatus calculates a correlation between a cyclic prefix and the last interval of a preamble or symbol, which is the same as the cyclic prefix, outputs the calculated correlation, and estimates a point at which the calculated correlation is maximal as the start point of the cyclic prefix. The frame start estimation apparatus then proceeds to step 370 to determine whether the number of estimated start points of a cyclic prefix reaches a predetermined number.
  • the final start point of a cyclic prefix may be an average of a plurality of estimated start points of the cyclic prefix. Since a communication system transmits frames whose number is sufficient for estimation of the start point of a frame, the frame start estimation apparatus estimates the start point of a cyclic prefix for a predetermined number of symbols.
  • the frame start estimation apparatus When the number of start points of a cyclic prefix, which are estimated in step 380, reaches a predetermined number, the frame start estimation apparatus combines the start points of a cyclic prefix, which are estimated in step 380, using Equation 2 to estimate a start point of a final frame.
  • the start point of a frame may be estimated by implementing only mode 1 as in step 320. However, it is also possible to implement mode 2 as in step 340 within a predetermined error range estimated based on the start point of a frame, resulting from implementation of mode 1, thereby estimating the more accurate start point of the frame.
  • the present invention it is possible to accurately estimate the start point of a frame even in a severe interference environment like a multi-sector environment by appropriately combining output results of a correlator having a variable window size and a variable delay for frame synchronization.
  • the foregoing present invention has been described by taking an example of a system adopting an IEEE 802.16-compliant OFDMA technique, however, can also be applied to a system that achieves frame synchronization based on a delay and a correlation using repeated patterns of a preamble.
  • the present invention can be applied to a general OFDM system having repeated patterns of a preamble.

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  • Computer Networks & Wireless Communication (AREA)
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Claims (2)

  1. Dispositif adapté pour estimer un départ d'une trame comprenant un préambule avec des schémas répétés et des symboles OFDM (Orthogonal Frequency Division Multiplexing), dans lequel le préambule et/ou les symboles OFDM comprennent un préfixe cyclique, dans un système de communication, le dispositif comprenant :
    un corrélateur (110) disposant d'une taille de fenêtre variable et d'un délai variable adapté pour fonctionner dans un parmi un premier et un deuxième mode en utilisant la taille de fenêtre variable et le délai variable, générant des premières valeurs de corrélation entre les schémas répétés du préambule pour une estimation du départ de la trame dans le premier mode et générant des deuxièmes valeurs de corrélation entre un préfixe cyclique et le dernier intervalle du préambule ou un symbole OFDM qui est identique au préfixe cyclique pour une estimation du départ d'un préfixe cyclique dans le deuxième mode ;
    un compteur (120) adapté pour incrémenter de 1 une valeur de compteur pour chaque échantillon de la trame et pour fournir la valeur de compteur au bloc de contrôle et à l'unité de sortie de point de valeur maximum ;
    un bloc de contrôle (140) adapté pour recevoir la valeur de compteur et adapté pour contrôler le corrélateur pour qu'il fonctionne dans le premier mode au cours d'un intervalle Ts d'une première trame, lorsque la première trame pour l'estimation du départ de la trame est reçue, et adapté pour contrôler le corrélateur pour qu'il fonctionne dans le deuxième mode au cours d'intervalles de trames indiqués par la première trame ;
    une unité de sortie de point de valeur maximum (120) adaptée pour recevoir les premières valeurs de corrélation et les deuxièmes valeurs de corrélation du corrélateur et la valeur de compteur du compteur, et adaptée pour générer une première valeur de compteur n0 selon une première valeur de corrélation maximum parmi les premières valeurs de corrélation et une deuxième valeur de compteur n1 selon une deuxième valeur de corrélation maximum parmi les deuxièmes valeurs de corrélation reçues du corrélateur au cours d'un intervalle temporel prédéterminé, dans laquelle la deuxième valeur de compteur n1 est un point de départ estimé du préfixe cyclique ; et
    une unité de sortie de point final (130) adaptée pour estimer un point de départ final de la trame utilisant les points de départ estimés du préfixe cyclique généré par l'unité de sortie de point de valeur maximum, et adapté pour générer le point de départ final estimé de la trame,
    dans lequel, si le nombre de schémas répétés est de trois, le corrélateur met en oeuvre le premier mode ayant la taille de fenêtre variable de 2L+CP et le délai variable de L qui font de la première valeur de corrélation une valeur maximale à un point de départ de chaque trame selon le contrôle du bloc de contrôle et le deuxième mode ayant la taille de fenêtre variable de CP et le délai variable de N qui font de la deuxième valeur de corrélation une valeur maximale à un point de départ du préfixe cyclique d'un parmi le préambule et le symbole OFDM selon le contrôle du bloc de contrôle, dans lequel le deuxième mode est mis en oeuvre après la mise en oeuvre du premier mode au cours d'au moins un intervalle de trame,
    où L est une longueur du préambule, CP est un intervalle du préfixe cyclique, et N est un d'un intervalle du préambule à l'exclusion de l'intervalle du préfixe cyclique et d'un intervalle du symbole OFDM à l'exclusion de l'intervalle du préfixe cyclique,
    dans lequel le bloc de contrôle reçoit la première valeur de compteur n0 selon la mise en oeuvre du premier mode et contrôle le corrélateur pour qu'il fonctionne dans le deuxième mode lorsqu'une valeur de compteur d'une trame suivante s'inscrit dans une plage d'erreur donnée Te de la première valeur de compteur n0,
    dans lequel le bloc de contrôle reçoit la deuxième valeur de compteur n1 selon la mise en oeuvre du deuxième mode et contrôle de manière répétée le corrélateur pour qu'il fonctionne dans le deuxième mode lorsqu'une valeur de compteur d'une trame suivante s'inscrit dans la plage d'erreur donnée Te ; et
    dans lequel, le bloc de contrôle est configuré pour remettre à 0 la première valeur de compteur n0 lorsque la première valeur de compteur n0 a atteint une valeur correspondant au premier intervalle de trame TS' et pour remettre à 0 la deuxième valeur de compteur n1 lorsque la deuxième valeur de compteur n1 au cours d'un prochain intervalle de trame atteint n0 - Te, où Te désigne la plage d'erreur de la première valeur de compteur n0,
    dans lequel l'unité de sortie de point final estime un point de départ ñf d'une trame finale pour des symboles jusqu'à m-1 utilisant l'équation suivante, n ˜ f = 1 M ∑ m = 1 M n m − m − 1 N + CP
    Figure imgb0007
     où M indique le nombre de points de départ du préfixe cyclique, N+CP indique l'intervalle entier d'un du préambule et du symbole OFDM, et nm indique le point de départ estimé du préfixe cyclique.
  2. Procédé pour estimer un début d'une trame comprenant un préambule avec des schémas répétés et des symboles OFDM (Orthogonal Frequency Division Multiplexing), dans lequel le préambule et/ou les symboles OFDM comprennent un préfixe cyclique, dans un système de communication, le procédé comprenant :
    la mise en oeuvre d'un premier mode au cours d'un intervalle d'une première trame, lorsque la première trame pour une estimation du départ de la trame est reçue, et une mise en oeuvre d'un deuxième mode au cours d'intervalles de trames indiqués par la première trame, la génération par un corrélateur de premières valeurs de corrélation entre les schémas répétés du préambule pour une estimation du départ de la trame dans le premier mode et la génération par le corrélateur de deuxièmes valeurs de corrélation entre un préfixe cyclique et le dernier intervalle du préambule ou un symbole OFDM qui est identique au préfixe cyclique pour une estimation du départ d'un préfixe cyclique dans le deuxième mode ;
    la réception des première et deuxième valeurs de corrélation et d'une valeur de compteur incrémentée de 1 pour chaque échantillon de la trame ;
    la génération d'une première valeur de compteur n0 selon une première valeur de corrélation maximum parmi les premières valeurs de corrélation et une deuxième valeur de compteur n1 selon une deuxième valeur de corrélation maximum parmi les deuxièmes valeurs de corrélation reçues au cours d'un intervalle temporel prédéterminé, dans lequel la deuxième valeur de compteur n1 selon la deuxième valeur de corrélation maximum est un point de départ estimé du préfixe cyclique ; et
    l'estimation d'un point de départ final de la trame utilisant les points de départ estimés du préfixe cyclique générés par l'unité de sortie de point de valeur maximum, et la génération du point de départ final estimé de la trame,
    dans lequel, si le nombre de schémas répétés est de trois, le corrélateur met en oeuvre le premier mode ayant la taille de fenêtre variable de 2L+CP et le délai variable de L qui font de la première valeur de corrélation une valeur maximale au point de départ de chaque tram et le deuxième mode ayant la taille de fenêtre variable de CP et le délai variable de N qui font de la deuxième valeur de corrélation une valeur maximale au point de départ du préfixe cyclique d'un parmi le préambule et le symbole OFDM selon le contrôle du bloc de contrôle, dans lequel le deuxième mode est mis en oeuvre après la mise en oeuvre du premier mode au cours d'au moins un intervalle de trame,
    où L est une longueur du préambule, CP est un intervalle du préfixe cyclique, et N est un d'un intervalle du préambule à l'exclusion de l'intervalle du préfixe cyclique et d'un intervalle du symbole OFDM à l'exclusion de l'intervalle du préfixe cyclique,
    comprenant en outre la réception de la première valeur de compteur n0 selon la mise en oeuvre du premier mode et le contrôle du corrélateur pour qu'il fonctionne dans le deuxième mode lorsqu'une valeur de compteur d'une trame suivante s'inscrit dans une plage d'erreur donnée Te de la première valeur de compteur n0 selon la première valeur de corrélation maximale,
    dans lequel la réception de la deuxième valeur de compteur n1 selon la mise en oeuvre du deuxième mode et le contrôle de manière répétée du corrélateur pour qu'il fonctionne dans le deuxième mode lorsqu'une valeur de compteur d'une trame suivante s'inscrit dans la plage d'erreur donnée Te et comprenant en outre la remise à 0 de la première valeur de compteur n0 lorsque la première valeur de compteur n0 est mise en correspondance avec le premier intervalle de trame Ts, et la remise à 0 de la deuxième valeur de compteur n1 lorsque la deuxième valeur de compteur (n1) au cours d'un prochain intervalle de trame atteint n0 - Te, où Te désigne la plage d'erreur de la première valeur de compteur n0,
    dans lequel l'estimation du point de départ final de la trame comprend un point de départ ñf d'une trame finale pour des symboles jusqu'à m-1 en utilisant l'équation suivante, n ˜ f = 1 M ∑ m = 1 M n m − m − 1 N + CP
    Figure imgb0008
     où M indique le nombre de points de départ du préfixe cyclique, N+CP indique l'intervalle entier d'un parmi le préambule et le symbole OFDM, et nm indique le point de départ estimé du préfixe cyclique.
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US7623582B2 (en) 2009-11-24
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KR100640472B1 (ko) 2006-10-30
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